textproduct: Quad Cities

KEY MESSAGES

- High certainty in oppressively humid conditions Sunday through Monday, with just how hot each afternoon dependent on any regional t-storm influences. Heat headlines continue for both days given forecast impactful metrics, including >70% chance of heat indices exceeding 100F on both days.

- Episodic semi-organized thunderstorms in the Upper Midwest late tonight trough the daytime Monday, some having a severe risk (levels 1-2 of 5), but low confidence on specifics in our forecast area where there are continued 20-30% chances.

SHORT TERM /THROUGH SUNDAY/

Issued at 300 PM CDT Sat Jul 25 2026

The rare July stratus continues to gradually lift and scour this Saturday afternoon. What's aiding this stratus is gradual isentropic ascent ahead of an incoming warm front, and this warm front will usher in the much warmer and especially humid air mass. Dew points in the mid to even upper 70s are anchored just upstream across the western half of Iowa into Missouri, and as these move in the air will have a more sultry feel this evening.

As is typical on the northern periphery of an expansive summer heat done, and this one characterized by a 500 mb height center of 598 dam over the front range, there is a favorable setup for some Upper Midwest storms late tonight. A seasonably strong upper to mid level jet and one to two disturbances are likely to develop some organized, mature storms in South Dakota, southwest Minnesota, and potentially into northwest Iowa later this evening. Thickness diffluence and the instability gradient would support any such clusters/complex to take a south of east turn as it approaches our longitude late tonight. The regional low-level jet (LLJ) is projected to be 20-30 kt, not the strongest LLJ for supporting a long-lived mature MCS. But the incoming EML and associated MUCAPE gradient (1,500-3,000 J/kg across our northern area by daybreak) has us concerned that either a weakening MCS or scattered development ahead of it may be seen into our CWA.

As highlighted by the 12Z HREF and REFS summarizing the morning CAMs, 20-40% of members indicate scattered thunderstorms making it as far southeast as our northern couple tiers of counties, and would not be surprised if some storms can do that, then there would be isolated festering storms through mid-late morning toward I-80. But the overall certainty in convection, while having trended up, still is <50%. Deep layer shear of 40 kt and the aforementioned MUCAPE support an isolated severe risk Sunday morning with any storms that are present. The most likely scenario for Sunday afternoon is that capping wins out and the area is free of convection.

Temperatures will have some dependence on the factors above, and there is more certainty in at least some convective debris clouds Sunday morning. With afternoon 925mb temperatures of 25-29C projected though, even some morning clouds probably won't thwart reaching at least 90F and if more sun then 94-95F is very much in play, especially with southwest extent in our CWA. Each degree warmer in a mid-upper 70s dew point environment such as will be in place Sunday requires considerably more energy, so 91-93F still seems the more probable high temperature for most locations. Heat index readings fall out at 102 to 110 across much of the area. No changes made to heat headlines for Sunday.

LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/

Issued at 300 PM CDT Sat Jul 25 2026

For Sunday night, there are indications of a short wave impulse moving southeast from the Upper Midwest into the western Great Lakes around the periphery of the heat dome. The nose of the LLJ moisture transport is more focused northeast of the area, although only slightly, and the CAM trend has been lesser coverage on Sunday night. Kinematics are conducive for organization (clusters or possibly a complex) of storms where they do develop and track. The timing though is challenging, and cannot rule out isolated activity Sunday evening due to the cap possibly being overcome in southern Wisconsin/northern Illinois. All in all continue the chance of storms, and tightened the PoP gradient on the western and southern edge.

For Monday, apart from morning convective influences, the pattern is a favorable one for very high heat indices (105-110), as characterized by: 1.) 925 mb temperatures of 25-30C, climatologically favoring at least mid 90s when well- mixed and no convective influences, 2.) widespread dew point reservoir of mid to upper 70s at peak evapotranspiration season, 3.) very warm starting point to the day, and 4.) strong suppression / capping signal for the afternoon. It is increasingly likely (>70% chance) with this setup that an Advisory or Warning will be needed for all counties on Monday, and that some, maybe most of the area, will be under a continuation of the Warning. By Monday night, the forcing is not coincident with the cold front, and capping is forecast to continue, so continue with low to non-mentionable PoPs in that time.

No changes made to the below Tuesday through Friday discussion.

Following the passage of storms with the cold front overnight into Tuesday, high pressure will build in on the northeast periphery of the upper level ridge. The cold front will help slightly lower heat indices into the mid-90s with the introduction of a drier airmass, though this heat will remain through both Tuesday and Wednesday as we remain under the influence of the ridge.

By midweek, the greatest question is when the ridge retrogrades and brings us back into the summertime storm track and grants us a reprieve from the heat.The majority of the guidance has this change towards the end of the period around Thursday and Friday, though there a few outliers that have it as early as Wednesday. With this return to the storm track, there is the potential for another system to pass through as soon as Friday, though changes in speed could have it arrive earlier.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 602 PM CDT Sat Jul 25 2026

MVFR cigs will remain for the next few hours, with a broken deck hovering around 2000-3000 ft. These clouds should scatter out by 03z throughout. Between 10-14z Sunday morning, we may see a weakening complex of storms pass through parts of the area. Currently, DBQ and CID seem to have the best chances, albeit only around 30%. Thus, opted for PROB30 groups at this time. Otherwise, confidence is too low to include at other terminals. Even if the showers/storms don't make it, some low stratus may work through the area, which may lower cigs as far south as MLI. This will be something to monitor during the overnight hours. Otherwise, we are not expecting much significant weather at this time.

Winds will remain light and largely out of the south/southeast through tonight, increasing slightly out of the southwest between 12-18z Sunday.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Extreme Heat Warning from 11 AM to 9 PM CDT Sunday for IAZ040>042-051>054-063>068-076>078-087>089-098-099. Extreme Heat Watch from Sunday evening through Monday evening for IAZ040>042-051>054-063>068-076>078-087>089-098-099. IL...Extreme Heat Warning from 11 AM to 9 PM CDT Sunday for ILZ009- 015>018-024>026-034-035. Extreme Heat Watch from Sunday evening through Monday evening for ILZ001-002-007-009-015>018-024>026-034-035. Heat Advisory from 11 AM to 9 PM CDT Sunday for ILZ001-002-007. MO...Extreme Heat Warning from 11 AM to 9 PM CDT Sunday for MOZ009- 010. Extreme Heat Watch from Sunday evening through Monday evening for MOZ009-010.